1. Field of the Invention
The present invention relates to a dedicated short-range communication mobile device for Intelligent transport systems, and more particularly to a dedicated short-range communication mobile device that can reduce dissipation and does not complicate communication control.
2. Description of the Related Art
Intelligent transport systems provide advantages to both drivers and road administrators by allowing a ground device provided on a ground side to communicate with a mobile device provided in a vehicle for various types of data transfer using a dedicated short-range communication (DSRC) system designed for communication within a limited range of road through radio waves in the microwave frequency region.
FIG. 7 is a partial block diagram showing a conventional dedicated short-range communication mobile device for an Intelligent transport system. In FIG. 7, reference numeral 1 denotes a transmission/reception antenna. Reference numeral 2 denotes a data transmission/reception circuit that transmits and receives data to and from a ground device (not shown) through the transmission/reception antenna 1. The data transmission/reception circuit 2 always searches a radio wave from the ground device through the transmission/reception antenna 1 while in operation. When the circuit 2 is ready for data transfer as the power of the searched radio wave has reached a predetermined strength so that the circuit 2 can start transmitting and receiving data to and from the ground device in accordance with a predetermined protocol. Reference numeral 3 denotes a first power supply circuit that supplies power to the data transmission/reception circuit 2. Reference numeral 4 denotes a fixed-value timer. Reference numeral 5 denotes power supply starting means that is operated by the fixed-value timer 4 after the elapse of a predetermined time interval to start the first power supply circuit 3. Reference numeral 6 denotes a second power supply circuit that supplies power to the fixed-value timer 4, the power supply starting means 5 and other devices.
Dedicated short-range communication in the Intelligent transport system is effected within a limited road range as described above. The data transmission/reception circuit 2 always searches a radio wave from the ground device while the vehicle is travelling, and upon detection of the radio wave from the ground device, starts data transfer with the ground device in accordance with a predetermined protocol.
After the data transmission/reception circuit 2 finishes a single round of data transfer with the ground device, the fixed-value timer 4 operates so that the data transmission/reception circuit 2 will not be started again in the same communication area until a predetermined time interval elapses. More specifically, after a single round of data transfer has been terminated, the first power supply circuit 3 stops supplying power to the data transmission/reception circuit 2, and after the elapse of the predetermined time interval, the fixed-value timer 4 operates the power supply starting means 5 so that the first power supply circuit 3 starts its operation again.
FIG. 8 is a partial block diagram showing another conventional dedicated short-range communication mobile device. In FIG. 8, reference numeral 7 denotes a variable-value timer that is set at a reference value contained in the data received from a ground device. That is, the ground device transmits to the mobile device a reference value corresponding to a communication area. The mobile device receives such reference value and sets the variable-value timer 7 at the received reference value. Therefore, when the communication area is wide, the variable-value timer 7 is set at a long time interval, whereas when the communication area is narrow, the timer 7 is set at a short time interval. Other configurational aspects of the device shown in FIG. 8 are the same as those of the device shown in FIG. 7.
With the aforementioned configuration, the conventional dedicated short-range communication mobile device prevents a second round of data transmission and reception within a single communication area.
However, the thus configured dedicated short-range communication mobile devices address a problem when the vehicle is travelling at a very slow velocity or is brought to a complete stop within a predetermined communication area due to, e.g., a traffic jam. That is, the problem is that, under such circumstances, even the mobile devices having the aforementioned configuration disadvantageously permit the data transmission/reception circuit 2 to start its operation again, and thus dissipation is increased. Further, the ground device is compelled to communicate with vehicles it does not have to communicate with, and thus a number of unnecessary communications complicate communication control. From this arises inconvenience that the ground device cannot communicate with the desired vehicle.
The present invention has been made to overcome the aforementioned problems, and its object is, therefore, to provide a dedicated short-range communication mobile device that can reduce dissipation and does not complicate communication control.
In order to achieve the above object, according to one aspect of the present invention, there is provided a dedicated short-range communication mobile device for Intelligent transport systems which comprises an antenna; a data transmission/reception circuit for transmitting and receiving data to and from a ground device through the antenna; a first power supply circuit for supplying power to the data transmission/reception circuit; received electric field strength detecting means for measuring a power level of a radio wave from the ground device received through the antenna; communication area detecting means for recognizing, as a communication area, an area in which the power level of the radio wave from the ground device exceeds a predetermined value based on an output of the received electric field strength detecting means; power supply starting means for starting the first power supply circuit based on an output of the communication area detecting means; and a second power supply circuit for supplying power to the received electric field strength detecting means, the communication area detecting means and the power supply starting means.
According to another aspect of the present invention, there is provided a dedicated short-range communication mobile device for Intelligent transport systems, wherein the output of the received electric field strength detecting means is inputted to the communication area detecting means through a filter for preventing fluctuations in received electric field strength to be caused by phasing of the radio wave from the ground device.
According to still another aspect of the present invention, there is provided a dedicated short-range communication mobile device for Intelligent transport systems, which has velocity detecting means for detecting a velocity of a vehicle at the time of data transmission and reception based on a trigger from the data transmission/reception circuit; and area end predicting means for calculating a travel distance based on an output of the velocity detecting means and predicting an end of a communication area.
According to a further aspect of the present invention, there is provided a dedicated short-range communication mobile device for Intelligent transport systems which comprises an antenna; a data transmission/reception circuit for transmitting and receiving data to and from a ground device through the antenna; a first power supply circuit for supplying power to the data transmission/reception circuit; velocity detecting means for detecting a velocity of a vehicle at the time of data transmission and reception based on a trigger from the data transmission/reception circuit; travel distance integrating means for integrating a travel distance based on an output of the velocity detecting means; communication area detecting means for recognizing a communication area by determining an end of the communication area when the travel distance exceeds a predetermined value; power supply starting means for starting the first power supply circuit based on an output of the communication area detecting means; and a second power supply circuit for supplying power to the velocity detecting means, the travel distance integrating means, the communication area detecting means and the power supply starting means.
According to a still further aspect of the present invention, there is provided a dedicated short-range communication mobile device for Intelligent transport systems which comprises an antenna; a data transmission/reception circuit for transmitting and receiving data to and from a ground device through the antenna; a first power supply circuit for supplying power to the data transmission/reception circuit; velocity detecting means for detecting a velocity of a vehicle at the time of data transmission and reception based on a trigger from the data transmission/reception circuit; a velocity corresponding timer that is set at a value in correspondence with an output of the velocity detecting means; communication area detecting means for recognizing a communication area based on an output of the velocity corresponding timer; power supply starting means for starting the first power supply circuit based on an output of the communication area detecting means; and a second power supply circuit for supplying power to the velocity detecting means, the travel distance integrating means, the communication area detecting means and the power supply starting means.